This invention relates to high speed, high pressure hydraulic pumping units, particularly opposed piston-type pumps for use in vehicular antilock brake systems (ABS) including those having integrated traction assist (TA) features, i.e., ABS/TA pumps, and the construction and placement of the check valves controlling fluid flow to and from the pump per se.
In any conventional ABS/TA system in use on vehicles today, there is generally provided an electric motor-driven opposed piston-type pumping unit for supplying pressurized brake fluid to any one of the brakes on instant, automatically controlled demand. The electrically-driven motor is a part of the ABS/TA unit and includes a drive shaft which will include one or more cam lobes. Transversely disposed of the drive shaft, generally at 180.degree. from one another, are a pair of pumping pistons within a respective pump body. The output of each pumping piston provides high pressure brake fluid, generally in the order of 2500 psi, to a respective segment of the braking system. In other words, in a conventional braking system for a four-wheel vehicle, the braking system is divided into two separate braking segments beginning at a dual-chambered master cylinder. Each segment provides the braking force to a predetermined pair of wheels. One segment may be to the left front-right rear wheels, for example, while the other segment provides the braking power to the right front-left rear wheels. The ABS/TA system is typically integrated into the vehicular braking system in the same manner, thereby providing antilock braking characteristics from each of the pair of pumping units to a respective one of the braking system segments. Likewise, traction assist capabilities are commonly added to the ABS/TA system in such a manner as to use the pump output for applying brake pressure to any one or more of the wheels to preclude wheel slip. This means increased use of the common pump, and added concern for the cost and performance attributes of the pump.
Due to the performance demanded of the ABS/TA unit, it is important that the pumping unit provide high pressure brake fluid to the system as efficiently and quickly as possible.
Further, it is important that the pumping unit be efficiently and effectively manufactured to meet applicable quality control and performance standards.